The present invention is based on Japanese Patent Application Nos.2001-000,931 and 2001-000,932, each content of which is incorporated by reference.
1. Field of the Invention
The present invention relates to a developing device of monocomponent development system which is used for developing a latent image formed on an image bearing member in image forming apparatuses, such as copying machines, printers and the like.
2. Description of the Related Art
Heretofore, the image forming apparatuses, such as copying machines, printers and the like, have employed a variety of developing devices for developing the latent image formed on the image bearing member.
As such a developing device, there have been known a developing device of two-component development system using a developer containing a carrier and a toner, and that of monocomponent development system using a developer free from the carrier.
The developing device of monocomponent development system is arranged as follows. Generally at some place in the course of transportation of a toner on a surface of a toner carrying member to a development region opposite to an image bearing member, a regulating member having a spring resilience or rubber elasticity is pressed against the surface of the toner carrying member thereby ensuring a proper amount of toner carried on the toner carrying member to the development region and triboelectrically charging the toner in a predetermined polarity.
The conventional toner carrying member generally comprises a metallic roller or a metallic roller formed with an elastic layer on its surface.
However, in the arrangement wherein the regulating member is pressed against the surface of the toner carrying member, such as formed of the metallic roller, for regulating the amount of toner transported to the development region, the toner is subjected to such a great load originating in a contact pressure from the regulating member that the toner particles on the surface of the toner carrying member are fractured to produce fine particles. Particularly when the development speed is increased for high-speed image forming process, there occurs severe toner fracture to produce a great amount of fine particles which will be gradually accumulated on the surface of the toner carrying member and fused thereto. As a result, the images so formed suffer density variations.
In the conventional toner carrying member wherein the metallic roller is formed with the elastic layer on its surface, as described above, the thickness of the elastic layer over the surface of the metallic roller is increased in order to prevent the toner fracture caused by the pressure contact by the regulating member.
Unfortunately in the case where the elastic layer over the surface of the metallic roller has a great thickness, the forming precisions of the toner carrying member is lowered. Particularly in an arrangement designed for an enhanced durability of the toner carrying member and for high-speed development, wherein the toner carrying member opposes the image bearing member in the development region via a required gap therebetween so as to provide for a develop process with the toner carrying member maintained in non-contact relation with the image bearing member, the gap between the toner carrying member and the image bearing member is so varied that the images cannot be developed in a stable manner. Hence, the resultant images suffer density variations or noises due to electrical leakage.
It is an object of the invention to solve the aforementioned problems encountered by the developing device of monocomponent development system.
More specifically, the object of the invention is to provide a developing device of monocomponent development system adapted to prevent the toner fracture caused by the pressure contact by the regulating member.
It is another object of the invention to provide a developing device of monocomponent development system adapted to avoid the degradation of the forming precisions of the toner carrying member.
It is still another object of the invention to provide a developing device of monocomponent development system in which the toner carrying member opposes the image bearing member in the development region via a required gap therebetween so as to provide for the development process with the toner carrying member maintained in non-contact relation with the image bearing member, the device adapted to develop images in a stable manner thereby ensuring a stable formation of favorable images over an extended period of time.
A first developing device according to the invention comprises a toner carrying member disposed opposite an image bearing member via a gap of 50 to 250 xcexcm therebetween, and including a conductive substrate and an elastic layer having a rubber hardness of not more than 70 degrees and a thickness of 7 to 50 xcexcm; and a regulating member pressed against a surface of the toner carrying member for regulating the amount of toner carried on the toner carrying member.
A second developing device according to the invention comprises a toner carrying member disposed opposite an image bearing member via a gap of 50 to 250 xcexcm therebetween, and including a conductive substrate and an elastic layer having a rubber hardness of not more than 70 degrees and a thickness of 7 to 50 xcexcm; a regulating member pressed against a surface of the toner carrying member for regulating the amount of toner carried on the toner carrying member; and a power source member for applying an electric field of 1xc3x97106 to 3xc3x97107 V/m between the toner carrying member and the regulating member in a direction to charge the toner in a predetermined polarity.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention.